Javier Casallas - Academia.edu (original) (raw)
Papers by Javier Casallas
2019 IEEE Electrical Insulation Conference (EIC)
IEEE Industrial Electronics Magazine, 2022
2021 IEEE 13th International Symposium on Diagnostics for Electrical Machines, Power Electronics and Drives (SDEMPED), 2021
Broken damper bars and shorted field winding turns degrade the starting and running performance o... more Broken damper bars and shorted field winding turns degrade the starting and running performance of industrial wound field synchronous motors (WFSMs), and can lead to a forced outage of the motor and driven process. Testing of WFSM rotor windings mainly relies on off-line tests, which cannot be performed frequently and are known to lack reliability. Shorted turns in the field winding can be detected on-line from the airgap flux measurement, but require a sensor to be installed on the stator bore. In this paper, a new test method for detecting and classifying damper and field winding faults based on electrical signals is proposed. The proposed method can provide remote testing during the motor starting transient without disassembling the motor. Test results on a 30 kW, salient pole WFSM show that the test method can provide reliable detection and classification of damper and field winding faults.
2019 IEEE 28th International Symposium on Industrial Electronics (ISIE), 2019
This paper focuses on the design of an advanced fault-tolerant control (FTC) scheme for accommoda... more This paper focuses on the design of an advanced fault-tolerant control (FTC) scheme for accommodating high-resistance (HR) connection faults in three-phase permanent magnet synchronous motor (PMSM) drives. Unlike existing works on HR faults which are limited to only fault diagnosis, this paper proposes FTC scheme to control the fault and provide safe operation of the drive. The proposed FTC scheme employs a higher-order sliding mode (HOSM) current-controller, which cancels the extra dynamics that are generated due to the HR connection fault in the considered PMSM current-model. The cancellation of extra dynamics provides tracking of actual current dynamics (d, q) to the reference currents. Moreover, the detection of HR connection fault in 3-phases of a PMSM will be shown with the help of asymmetry (which occurs due to HR connection) in the currents. Experimental results followed by simulations for various cases of additional phase resistances are presented to demonstrate the effectiveness of proposed FTC scheme.
IEEE Transactions on Industry Applications, 2020
Lately, the monitoring and analysis of the induction motor stray flux has been a modern trend and... more Lately, the monitoring and analysis of the induction motor stray flux has been a modern trend and significant research work was accomplished. Most papers have focused on the monitoring of rotor electrical faults around the fundamental stray flux signature, imitating in this way the traditional Motor Current Signature Analysis (MCSA). However, such signatures may still have some disadvantages leading to false alarms. This is the motivation behind the use of alternative signatures such as, in this particular case, the mechanical frequency. The existence of the mechanical frequency in the stator current is still the best signature for detection of the mixed rotor eccentricity fault and load imbalances. Even healthy motors present this harmonic due to some low-level inherent eccentricity and inherent load oscillations. Despite that, it will be shown for the first time in this paper that the mechanical frequency associated harmonics in the stray flux is possible to originate purely from rotor electrical faults. Those signatures present significant sensitivity to the broken bar fault severity. Moreover, they are advantageous for low load operation compared to traditional signatures. Finally, the sidebands of the mechanical frequency related harmonics are very sensitive to the broken rotor bar fault while quite immune to the number of the rotor bars.
IEEE Industrial Electronics Magazine, 2020
The limitations of thermal, vibration, or electrical monitoring of electric machines such as fals... more The limitations of thermal, vibration, or electrical monitoring of electric machines such as false indications, low sensitivity, and difficulty of fault interpretation have recently been exposed. This has led to a shift in the direction in research towards applying new techniques for improving the reliability of condition monitoring. With the changing environment, the purpose of this article is to provide an overview of the recent trend in the industrial demand and research activity in condition monitoring technology. The new developments in insulation testing, electrical testing, flux analysis, transient analysis, and fault prognostics are summarized. The future challenges and recommendations for future work for the new technologies are also stated to support researchers target research/development efforts according to industrial needs.
IEEE/ASME Transactions on Mechatronics, 2020
Online monitoring of various faults that are associated with the permanent magnet synchronous mot... more Online monitoring of various faults that are associated with the permanent magnet synchronous motor (PMSM) is receiving much attention with the increasing demand in PMSM applications. Mechanical load imbalance is one of the mechanical defects that causes increase in the torque ripple, motor vibration, and can lead to accelerated wear and unstable drive operation, if the fault is undetected. Unlike existing methods that are limited to detection of rotor defects, in this article, a novel composite-control scheme is designed to estimate and compensate for the load torque disturbance (produced due to load imbalance) in the feedforward compensation design. It is shown that the proposed design with the feedback control law provides accurate compensation of load torque disturbance and achieves high-precision speed control (improved tracking performance up to 90% and smaller convergence time of up to 70%). Simulations as well as experimental testing validate the effectiveness and reliability of the proposed scheme.
La Direccion Nacional de Investigacion e Innovacion invita a los docentes investigadores a partic... more La Direccion Nacional de Investigacion e Innovacion invita a los docentes investigadores a participar en esta iniciativa para la apropiacion social del conocimiento en medio de la coyuntura que nos aboca a trabajar juntos y a compartir saberes a las comunidades. Serie Podcast "Mi ejercicio academico vs. Covid-19" Introduccion: "La apropiacion social se entiende como un proceso y practica social de construccion colectiva de conocimiento, cuyos integrantes pueden ser individuos, organizaciones o comunidades, que se involucran en interacciones tendientes a intercambiar saberes y experiencias." (Colciencias, 2019, p.77). Objetivo: Consolidar productos de apropiacion social del conocimiento de todos los grupos de investigacion USTA.
IEEE Transactions on Industry Applications, 2018
V-belt-pulley couplings are commonly used for speed reduction in induction motor driven industria... more V-belt-pulley couplings are commonly used for speed reduction in induction motor driven industrial applications since they provide flexible transmission of power at low cost. However, they are susceptible to mechanical defects such as belt wear or crack that can cause slippage or damage of the belt and lead to decrease in efficiency and lifetime of the system. There are many limitations to applying existing tests such as visual inspection, thermal or mechanical monitoring as they require visual or physical access to the system and/or costly sensors. Considering the large quantity of belt-pulley systems employed in industry, the impact of the economic loss incurred by lowefficiency operation and unplanned process outages is significant. In this paper, electrical monitoring of belt-pulley coupling defects based on the analysis and trending of the stator current frequency spectrum under steady-state and starting conditions is presented. The proposed method is verified on 1) 6.6 kV motor driven pulpers, and on a 2) custom-built motor driven air compressor with speed reduction belt-pulleys under controlled fault conditions. It is shown that the proposed method can provide automated, remote, and safe detection of belt-pulley defects based on existing current measurements for improving system reliability and efficiency. It is also shown that the proposed method can be applied to vibration measurements for motors where vibration sensors are installed.
IEEE Transactions on Industry Applications, 2018
The recent trend in squirrel cage induction motor manufacturing is to replace fabricated copper r... more The recent trend in squirrel cage induction motor manufacturing is to replace fabricated copper rotors with aluminum die-cast rotors to reduce manufacturing cost to stay competitive in the global market. Porosity in aluminum die-cast squirrel cage rotors is inevitably introduced during the die cast process. Porosity can cause degradation in motor performance and can lead to a forced outage causing irreversible damage in extreme cases. Many off-line and on-line quality assurance test methods have been developed and applied for assessment of rotor quality. However, years of experience with the existing test methods revealed that they are not suitable for quality testing or capable of providing a quantitative assessment of rotor porosity with sufficient sensitivity. In this paper, a new off-line test method capable of providing sensitive assessment of rotor porosity is proposed. It is shown that rotors with minor and distributed porosity that are difficult to detect with other tests can be screened out during manufacturing. The proposed method is verified through a 3 dimensional finite element analysis and experimental testing on closed and semi-open slot aluminum die cast rotors of 5.5 kW induction motors with porosity.
2016 IEEE Energy Conversion Congress and Exposition (ECCE), 2016
Motor current signature analysis (MCSA) has recently become widespread in industry for on-line de... more Motor current signature analysis (MCSA) has recently become widespread in industry for on-line detection of rotor cage faults in induction motors for preventing forced outages. Although it can provide low cost, remote monitoring of rotor faults, cases of false indications have been reported, where the causes of some false indications are still unknown. It is shown for the first time in this work that high-amplitude blade pass frequency (BPF) vibrations produced in pumps, fans, or compressors can cause false rotor fault indications, if the number of motor poles is an integer multiple of the number of blades. The influence of BPF vibration on MCSA based rotor fault detection is analyzed, and it is shown that the interaction between BPF vibration and rotor faults can produce false positive and negative fault indications. Alternative test methods capable of separating the influence of the BPF vibration and rotor faults are suggested for avoiding false MCSA alarms. The claims made in the paper are verified experimentally on a custom-built 380 V induction motor-centrifugal pump system setup.
IEEE Transactions on Industry Applications, 2017
HAND 11(1S) for CTS. We evaluated patients' decisional conflict regarding their decision for surg... more HAND 11(1S) for CTS. We evaluated patients' decisional conflict regarding their decision for surgery. We also evaluated patients' knowledge about the disease and the perceived functional status as measured by the Disabilities of Arm, Shoulder and Hand (DASH) Questionnaire. Results: There was no difference in the Decisional Conflict Scale between both groups. Patients who viewed the decision aid had significantly better knowledge of CTS than those who did not. There was no correlation between the knowledge level and the Decisional Conflict Scale. However, higher DASH scores were correlated with lower decisional conflict. Conclusions: This study found that a decision aid does not reduce decisional conflict in patients with CTS, although it can help the patients be better informed. This study suggests that effective doctor-patient communication continues to be the most important way to reduce the decisional conflict in patients with CTS, and should be more emphasized for patients with less severe symptoms, as they have greater decisional conflict than those with severe symptoms.
2015 IEEE Energy Conversion Congress and Exposition (ECCE), 2015
Stator-slot magnetic wedges are used instead of conventional epoxy glass wedges in large, high-ou... more Stator-slot magnetic wedges are used instead of conventional epoxy glass wedges in large, high-output induction motors since the motor efficiency and power factor can be improved. However, cases of loose or missing magnetic wedges due to their weak mechanical strength have recently been increasingly reported. Although missing wedges can deteriorate motor performance and reliability, there is currently no test method accepted in the field for wedge quality assessment other than offline, disassembled visual inspection. In this paper, a new in-service method for monitoring the magnetic wedge condition in induction motors based on the negative-sequence information is proposed. The new method is developed based on the analysis of the dynamic model of the induction motor with missing magnetic slot wedges, derived in this paper. The proposed method is verified on a finite-element (FE) model of a 6.6-kV, 1850-kW induction motor. It is also verified experimentally on a 6.6-kV, 220-kW induction motor operating in the field with missing wedges (before and after rewedging), and on a 380-V, 5.5-kW induction motor with custom-built, removable magnetic wedges. It is shown that the proposed method can provide online detection of missing magnetic wedges, which can help reduce maintenance costs and risk of degradation in motor performance.
IEEE Transactions on Industry Applications, 2016
Motor current signature analysis (MCSA) has become an essential part of the preventive maintenanc... more Motor current signature analysis (MCSA) has become an essential part of the preventive maintenance program for monitoring the condition of the rotor cage in medium-voltage induction motors in the pulp and paper industry. However, many cases of false indications due to interference from the motor or the load have been reported. False indications can result in unnecessary inspection and outage costs (false positives) or major repair/replacement costs and loss of production (false negatives). The objective of this paper is to present the potential root causes of false indications and provide guidelines on how commercially available offline and online tests can be applied for identifying false indications from a field engineers' perspective. Case studies of false MCSA indications and results of alternative commercial tests for improving the reliability of the diagnosis are provided through measurements on 6.6-kV and laboratory motor samples. Finally, new test methods under research and development for reliable rotor fault detection are summarized, and unresolved problems are listed. This paper is expected to help field maintenance engineers prevent unnecessary motor inspection and forced outages and guide researchers target future research toward industrial needs.
IMF Working Papers, 2007
This Working Paper should not be reported as representing the views of the IMF. The views express... more This Working Paper should not be reported as representing the views of the IMF. The views expressed in this Working Paper are those of the author(s) and do not necessarily represent those of the IMF or IMF policy. Working Papers describe research in progress by the author(s) and are published to elicit comments and to further debate. By using a simple intertemporal model of the current account, I show that the exchange rate elasticity of the trade balance would ceteris paribus be smaller for countries with higher government spending ratios (relative to GDP) and with more limited scope for private consumption smoothing. This finding may have important implications for the design of adjustment programs and for resolving current global imbalances. It could also help explain and reconcile mixed empirical findings on trade elasticities.
2012 IEEE Energy Conversion Congress and Exposition (ECCE), 2012
ABSTRACT Rotor fault diagnosis of induction machines is commonly realized through Motor Current S... more ABSTRACT Rotor fault diagnosis of induction machines is commonly realized through Motor Current Signature Analysis (MCSA), i.e., by classical spectrum analysis of the input currents. However, this technique may fail in the case of outer cage damage of double cage induction motors, due to the small current circulation in the rated operating conditions. The situation is more complicated under time-varying conditions, where the typical Rotor Fault Frequency Components (RFFCs), which appear in the phase current spectrum of faulty motors, are spread in a bandwidth proportional to the speed variation and are difficult to detect accurately. A new diagnosis method based on the combined use of Double-Frequency Sliding (DFS) and Discrete Wavelet Transform (DWT) is proposed here for the analysis of the stator phase current. A experimental study on a copper-made double cage separate end ring rotor shows the validity of the proposed approach, leading to an effective diagnosis procedure for fault detection in double cage motors under time-varying conditions.
2014 International Conference on Electrical Machines (ICEM), 2014
ABSTRACT Large induction motors contain axial air ducts in their rotor body for cooling purposes.... more ABSTRACT Large induction motors contain axial air ducts in their rotor body for cooling purposes. It has been noted lately that, the presence of the rotor air ducts affects the rotating magnetic field by introducing asymmetries. Those asymmetries produce higher harmonic content in the induction motor electromagnetic variables, same like the broken bar fault. So, the diagnostic procedure of a healthy motor with axial rotor air ducts could lead to a false broken bar fault alarm, which leads to unnecessary inspection cost, as well a significant cost because of the production process interruption for the motor inspection. In this paper, it is shown that the higher harmonic index of the electromagnetic torque can reliably be used to distinguish the healthy from the broken bar case reliably in induction motors with rotor axial air ducts.
IEEE Transactions on Industry Applications, 2014
ABSTRACT The recent trend in large ac machines is to employ magnetic stator slot wedges for impro... more ABSTRACT The recent trend in large ac machines is to employ magnetic stator slot wedges for improving the motor efficiency, power factor, and power density. The mechanical strength of magnetic wedges is weak compared to the epoxy glass wedges, and many cases of loose and missing wedges have recently been increasingly reported. Magnetic wedge failure deteriorates the performance and reliability of the motor, but there is no method available for testing the wedge quality other than visual inspection after rotor removal. Monitoring of overall wedge condition without motor disassembly can help reduce the cost of maintenance and risk of degradation in performance. In this paper, a new off-line standstill test method for detecting magnetic wedge problems for ac machines without motor disassembly is proposed. An experimental study on 380 V, 5.5 kW and 6.6 kV, 3.4 MW motors with magnetic wedges is performed to verify the effectiveness of the new test method. It is shown that the new method can provide reliable monitoring of magnetic wedge problems over time, independent of other faults or motor design.
IEEE Transactions on Industry Applications, 2005
An advanced technique for detecting incipient inter-laminar insulation failure in stator cores of... more An advanced technique for detecting incipient inter-laminar insulation failure in stator cores of large electric machines is proposed in this paper. The proposed scheme is an offline method based on low flux stator core excitation that employs a new probe. An iron-core probe is placed in the wedge depression area of the stator and scanned axially to detect the variation
IEEE Transactions on Industry Applications, 2009
A high-resistance (R) connection in an induction-motor electrical circuit results in localized ov... more A high-resistance (R) connection in an induction-motor electrical circuit results in localized overheating and supply-voltage unbalance, which leads to a decreased efficiency and reliability and an increased fire hazard in the electrical distribution system and motor. Therefore, it is important to monitor and correct high-R connections for a reliable, efficient, and safe operation of the industrial facility. This paper focuses
2019 IEEE Electrical Insulation Conference (EIC)
IEEE Industrial Electronics Magazine, 2022
2021 IEEE 13th International Symposium on Diagnostics for Electrical Machines, Power Electronics and Drives (SDEMPED), 2021
Broken damper bars and shorted field winding turns degrade the starting and running performance o... more Broken damper bars and shorted field winding turns degrade the starting and running performance of industrial wound field synchronous motors (WFSMs), and can lead to a forced outage of the motor and driven process. Testing of WFSM rotor windings mainly relies on off-line tests, which cannot be performed frequently and are known to lack reliability. Shorted turns in the field winding can be detected on-line from the airgap flux measurement, but require a sensor to be installed on the stator bore. In this paper, a new test method for detecting and classifying damper and field winding faults based on electrical signals is proposed. The proposed method can provide remote testing during the motor starting transient without disassembling the motor. Test results on a 30 kW, salient pole WFSM show that the test method can provide reliable detection and classification of damper and field winding faults.
2019 IEEE 28th International Symposium on Industrial Electronics (ISIE), 2019
This paper focuses on the design of an advanced fault-tolerant control (FTC) scheme for accommoda... more This paper focuses on the design of an advanced fault-tolerant control (FTC) scheme for accommodating high-resistance (HR) connection faults in three-phase permanent magnet synchronous motor (PMSM) drives. Unlike existing works on HR faults which are limited to only fault diagnosis, this paper proposes FTC scheme to control the fault and provide safe operation of the drive. The proposed FTC scheme employs a higher-order sliding mode (HOSM) current-controller, which cancels the extra dynamics that are generated due to the HR connection fault in the considered PMSM current-model. The cancellation of extra dynamics provides tracking of actual current dynamics (d, q) to the reference currents. Moreover, the detection of HR connection fault in 3-phases of a PMSM will be shown with the help of asymmetry (which occurs due to HR connection) in the currents. Experimental results followed by simulations for various cases of additional phase resistances are presented to demonstrate the effectiveness of proposed FTC scheme.
IEEE Transactions on Industry Applications, 2020
Lately, the monitoring and analysis of the induction motor stray flux has been a modern trend and... more Lately, the monitoring and analysis of the induction motor stray flux has been a modern trend and significant research work was accomplished. Most papers have focused on the monitoring of rotor electrical faults around the fundamental stray flux signature, imitating in this way the traditional Motor Current Signature Analysis (MCSA). However, such signatures may still have some disadvantages leading to false alarms. This is the motivation behind the use of alternative signatures such as, in this particular case, the mechanical frequency. The existence of the mechanical frequency in the stator current is still the best signature for detection of the mixed rotor eccentricity fault and load imbalances. Even healthy motors present this harmonic due to some low-level inherent eccentricity and inherent load oscillations. Despite that, it will be shown for the first time in this paper that the mechanical frequency associated harmonics in the stray flux is possible to originate purely from rotor electrical faults. Those signatures present significant sensitivity to the broken bar fault severity. Moreover, they are advantageous for low load operation compared to traditional signatures. Finally, the sidebands of the mechanical frequency related harmonics are very sensitive to the broken rotor bar fault while quite immune to the number of the rotor bars.
IEEE Industrial Electronics Magazine, 2020
The limitations of thermal, vibration, or electrical monitoring of electric machines such as fals... more The limitations of thermal, vibration, or electrical monitoring of electric machines such as false indications, low sensitivity, and difficulty of fault interpretation have recently been exposed. This has led to a shift in the direction in research towards applying new techniques for improving the reliability of condition monitoring. With the changing environment, the purpose of this article is to provide an overview of the recent trend in the industrial demand and research activity in condition monitoring technology. The new developments in insulation testing, electrical testing, flux analysis, transient analysis, and fault prognostics are summarized. The future challenges and recommendations for future work for the new technologies are also stated to support researchers target research/development efforts according to industrial needs.
IEEE/ASME Transactions on Mechatronics, 2020
Online monitoring of various faults that are associated with the permanent magnet synchronous mot... more Online monitoring of various faults that are associated with the permanent magnet synchronous motor (PMSM) is receiving much attention with the increasing demand in PMSM applications. Mechanical load imbalance is one of the mechanical defects that causes increase in the torque ripple, motor vibration, and can lead to accelerated wear and unstable drive operation, if the fault is undetected. Unlike existing methods that are limited to detection of rotor defects, in this article, a novel composite-control scheme is designed to estimate and compensate for the load torque disturbance (produced due to load imbalance) in the feedforward compensation design. It is shown that the proposed design with the feedback control law provides accurate compensation of load torque disturbance and achieves high-precision speed control (improved tracking performance up to 90% and smaller convergence time of up to 70%). Simulations as well as experimental testing validate the effectiveness and reliability of the proposed scheme.
La Direccion Nacional de Investigacion e Innovacion invita a los docentes investigadores a partic... more La Direccion Nacional de Investigacion e Innovacion invita a los docentes investigadores a participar en esta iniciativa para la apropiacion social del conocimiento en medio de la coyuntura que nos aboca a trabajar juntos y a compartir saberes a las comunidades. Serie Podcast "Mi ejercicio academico vs. Covid-19" Introduccion: "La apropiacion social se entiende como un proceso y practica social de construccion colectiva de conocimiento, cuyos integrantes pueden ser individuos, organizaciones o comunidades, que se involucran en interacciones tendientes a intercambiar saberes y experiencias." (Colciencias, 2019, p.77). Objetivo: Consolidar productos de apropiacion social del conocimiento de todos los grupos de investigacion USTA.
IEEE Transactions on Industry Applications, 2018
V-belt-pulley couplings are commonly used for speed reduction in induction motor driven industria... more V-belt-pulley couplings are commonly used for speed reduction in induction motor driven industrial applications since they provide flexible transmission of power at low cost. However, they are susceptible to mechanical defects such as belt wear or crack that can cause slippage or damage of the belt and lead to decrease in efficiency and lifetime of the system. There are many limitations to applying existing tests such as visual inspection, thermal or mechanical monitoring as they require visual or physical access to the system and/or costly sensors. Considering the large quantity of belt-pulley systems employed in industry, the impact of the economic loss incurred by lowefficiency operation and unplanned process outages is significant. In this paper, electrical monitoring of belt-pulley coupling defects based on the analysis and trending of the stator current frequency spectrum under steady-state and starting conditions is presented. The proposed method is verified on 1) 6.6 kV motor driven pulpers, and on a 2) custom-built motor driven air compressor with speed reduction belt-pulleys under controlled fault conditions. It is shown that the proposed method can provide automated, remote, and safe detection of belt-pulley defects based on existing current measurements for improving system reliability and efficiency. It is also shown that the proposed method can be applied to vibration measurements for motors where vibration sensors are installed.
IEEE Transactions on Industry Applications, 2018
The recent trend in squirrel cage induction motor manufacturing is to replace fabricated copper r... more The recent trend in squirrel cage induction motor manufacturing is to replace fabricated copper rotors with aluminum die-cast rotors to reduce manufacturing cost to stay competitive in the global market. Porosity in aluminum die-cast squirrel cage rotors is inevitably introduced during the die cast process. Porosity can cause degradation in motor performance and can lead to a forced outage causing irreversible damage in extreme cases. Many off-line and on-line quality assurance test methods have been developed and applied for assessment of rotor quality. However, years of experience with the existing test methods revealed that they are not suitable for quality testing or capable of providing a quantitative assessment of rotor porosity with sufficient sensitivity. In this paper, a new off-line test method capable of providing sensitive assessment of rotor porosity is proposed. It is shown that rotors with minor and distributed porosity that are difficult to detect with other tests can be screened out during manufacturing. The proposed method is verified through a 3 dimensional finite element analysis and experimental testing on closed and semi-open slot aluminum die cast rotors of 5.5 kW induction motors with porosity.
2016 IEEE Energy Conversion Congress and Exposition (ECCE), 2016
Motor current signature analysis (MCSA) has recently become widespread in industry for on-line de... more Motor current signature analysis (MCSA) has recently become widespread in industry for on-line detection of rotor cage faults in induction motors for preventing forced outages. Although it can provide low cost, remote monitoring of rotor faults, cases of false indications have been reported, where the causes of some false indications are still unknown. It is shown for the first time in this work that high-amplitude blade pass frequency (BPF) vibrations produced in pumps, fans, or compressors can cause false rotor fault indications, if the number of motor poles is an integer multiple of the number of blades. The influence of BPF vibration on MCSA based rotor fault detection is analyzed, and it is shown that the interaction between BPF vibration and rotor faults can produce false positive and negative fault indications. Alternative test methods capable of separating the influence of the BPF vibration and rotor faults are suggested for avoiding false MCSA alarms. The claims made in the paper are verified experimentally on a custom-built 380 V induction motor-centrifugal pump system setup.
IEEE Transactions on Industry Applications, 2017
HAND 11(1S) for CTS. We evaluated patients' decisional conflict regarding their decision for surg... more HAND 11(1S) for CTS. We evaluated patients' decisional conflict regarding their decision for surgery. We also evaluated patients' knowledge about the disease and the perceived functional status as measured by the Disabilities of Arm, Shoulder and Hand (DASH) Questionnaire. Results: There was no difference in the Decisional Conflict Scale between both groups. Patients who viewed the decision aid had significantly better knowledge of CTS than those who did not. There was no correlation between the knowledge level and the Decisional Conflict Scale. However, higher DASH scores were correlated with lower decisional conflict. Conclusions: This study found that a decision aid does not reduce decisional conflict in patients with CTS, although it can help the patients be better informed. This study suggests that effective doctor-patient communication continues to be the most important way to reduce the decisional conflict in patients with CTS, and should be more emphasized for patients with less severe symptoms, as they have greater decisional conflict than those with severe symptoms.
2015 IEEE Energy Conversion Congress and Exposition (ECCE), 2015
Stator-slot magnetic wedges are used instead of conventional epoxy glass wedges in large, high-ou... more Stator-slot magnetic wedges are used instead of conventional epoxy glass wedges in large, high-output induction motors since the motor efficiency and power factor can be improved. However, cases of loose or missing magnetic wedges due to their weak mechanical strength have recently been increasingly reported. Although missing wedges can deteriorate motor performance and reliability, there is currently no test method accepted in the field for wedge quality assessment other than offline, disassembled visual inspection. In this paper, a new in-service method for monitoring the magnetic wedge condition in induction motors based on the negative-sequence information is proposed. The new method is developed based on the analysis of the dynamic model of the induction motor with missing magnetic slot wedges, derived in this paper. The proposed method is verified on a finite-element (FE) model of a 6.6-kV, 1850-kW induction motor. It is also verified experimentally on a 6.6-kV, 220-kW induction motor operating in the field with missing wedges (before and after rewedging), and on a 380-V, 5.5-kW induction motor with custom-built, removable magnetic wedges. It is shown that the proposed method can provide online detection of missing magnetic wedges, which can help reduce maintenance costs and risk of degradation in motor performance.
IEEE Transactions on Industry Applications, 2016
Motor current signature analysis (MCSA) has become an essential part of the preventive maintenanc... more Motor current signature analysis (MCSA) has become an essential part of the preventive maintenance program for monitoring the condition of the rotor cage in medium-voltage induction motors in the pulp and paper industry. However, many cases of false indications due to interference from the motor or the load have been reported. False indications can result in unnecessary inspection and outage costs (false positives) or major repair/replacement costs and loss of production (false negatives). The objective of this paper is to present the potential root causes of false indications and provide guidelines on how commercially available offline and online tests can be applied for identifying false indications from a field engineers' perspective. Case studies of false MCSA indications and results of alternative commercial tests for improving the reliability of the diagnosis are provided through measurements on 6.6-kV and laboratory motor samples. Finally, new test methods under research and development for reliable rotor fault detection are summarized, and unresolved problems are listed. This paper is expected to help field maintenance engineers prevent unnecessary motor inspection and forced outages and guide researchers target future research toward industrial needs.
IMF Working Papers, 2007
This Working Paper should not be reported as representing the views of the IMF. The views express... more This Working Paper should not be reported as representing the views of the IMF. The views expressed in this Working Paper are those of the author(s) and do not necessarily represent those of the IMF or IMF policy. Working Papers describe research in progress by the author(s) and are published to elicit comments and to further debate. By using a simple intertemporal model of the current account, I show that the exchange rate elasticity of the trade balance would ceteris paribus be smaller for countries with higher government spending ratios (relative to GDP) and with more limited scope for private consumption smoothing. This finding may have important implications for the design of adjustment programs and for resolving current global imbalances. It could also help explain and reconcile mixed empirical findings on trade elasticities.
2012 IEEE Energy Conversion Congress and Exposition (ECCE), 2012
ABSTRACT Rotor fault diagnosis of induction machines is commonly realized through Motor Current S... more ABSTRACT Rotor fault diagnosis of induction machines is commonly realized through Motor Current Signature Analysis (MCSA), i.e., by classical spectrum analysis of the input currents. However, this technique may fail in the case of outer cage damage of double cage induction motors, due to the small current circulation in the rated operating conditions. The situation is more complicated under time-varying conditions, where the typical Rotor Fault Frequency Components (RFFCs), which appear in the phase current spectrum of faulty motors, are spread in a bandwidth proportional to the speed variation and are difficult to detect accurately. A new diagnosis method based on the combined use of Double-Frequency Sliding (DFS) and Discrete Wavelet Transform (DWT) is proposed here for the analysis of the stator phase current. A experimental study on a copper-made double cage separate end ring rotor shows the validity of the proposed approach, leading to an effective diagnosis procedure for fault detection in double cage motors under time-varying conditions.
2014 International Conference on Electrical Machines (ICEM), 2014
ABSTRACT Large induction motors contain axial air ducts in their rotor body for cooling purposes.... more ABSTRACT Large induction motors contain axial air ducts in their rotor body for cooling purposes. It has been noted lately that, the presence of the rotor air ducts affects the rotating magnetic field by introducing asymmetries. Those asymmetries produce higher harmonic content in the induction motor electromagnetic variables, same like the broken bar fault. So, the diagnostic procedure of a healthy motor with axial rotor air ducts could lead to a false broken bar fault alarm, which leads to unnecessary inspection cost, as well a significant cost because of the production process interruption for the motor inspection. In this paper, it is shown that the higher harmonic index of the electromagnetic torque can reliably be used to distinguish the healthy from the broken bar case reliably in induction motors with rotor axial air ducts.
IEEE Transactions on Industry Applications, 2014
ABSTRACT The recent trend in large ac machines is to employ magnetic stator slot wedges for impro... more ABSTRACT The recent trend in large ac machines is to employ magnetic stator slot wedges for improving the motor efficiency, power factor, and power density. The mechanical strength of magnetic wedges is weak compared to the epoxy glass wedges, and many cases of loose and missing wedges have recently been increasingly reported. Magnetic wedge failure deteriorates the performance and reliability of the motor, but there is no method available for testing the wedge quality other than visual inspection after rotor removal. Monitoring of overall wedge condition without motor disassembly can help reduce the cost of maintenance and risk of degradation in performance. In this paper, a new off-line standstill test method for detecting magnetic wedge problems for ac machines without motor disassembly is proposed. An experimental study on 380 V, 5.5 kW and 6.6 kV, 3.4 MW motors with magnetic wedges is performed to verify the effectiveness of the new test method. It is shown that the new method can provide reliable monitoring of magnetic wedge problems over time, independent of other faults or motor design.
IEEE Transactions on Industry Applications, 2005
An advanced technique for detecting incipient inter-laminar insulation failure in stator cores of... more An advanced technique for detecting incipient inter-laminar insulation failure in stator cores of large electric machines is proposed in this paper. The proposed scheme is an offline method based on low flux stator core excitation that employs a new probe. An iron-core probe is placed in the wedge depression area of the stator and scanned axially to detect the variation
IEEE Transactions on Industry Applications, 2009
A high-resistance (R) connection in an induction-motor electrical circuit results in localized ov... more A high-resistance (R) connection in an induction-motor electrical circuit results in localized overheating and supply-voltage unbalance, which leads to a decreased efficiency and reliability and an increased fire hazard in the electrical distribution system and motor. Therefore, it is important to monitor and correct high-R connections for a reliable, efficient, and safe operation of the industrial facility. This paper focuses